Inhibition of leukotriene biosynthesis has been an active area of pharmaceutical research for many years. The leukotrienes constitute a group of locally acting hormones, produced in living systems from arachidonic acid. Leukotrienes are potent contractile and inflammatory mediators derived by enzymatic oxygenation of arachidonic acid by 5-lipoxygenase. One class of leukotriene biosynthesis inhibitors are those known to act through inhibition of 5-lipoxygenase (5-LO).
The major leukotrienes are Leukotriene B4 (abbreviated as LTB4), LTC4, LTD4 and LTE4. The biosynthesis of these leukotrienes begins with the action of the enzyme 5-lipoxygenases on arachidonic acid to produce the epoxide known as Leukotriene A4 (LTA4), which is converted to the other leukotrienes by subsequent enzymatic steps. Further details of the biosynthesis as well as the metabolism of the leukotrienes are to be found in the book Leukotrienes and Lipoxygenases, ed. J. Rokach, Elsevier, Amsterdam (1989). The actions of the leukotrienes in living systems and their contribution to various diseases states are also discussed in the book by Rokach.
In general, 5-LO inhibitors have been sought for the treatment of allergic rhinitis, asthma and inflammatory conditions including arthritis. One example of a 5-LO inhibitor is the marketed drug zileuton (ZYLOFT®) which is indicated for the treatment of asthma. More recently, it has been reported that 5-LO may be an important contributor to the atherogenic process; see Mehrabian, M. et al., Circulation Research, Jul. 26, 2002 91(2):120-126.
Despite significant therapeutic advances in the treatment and prevention of conditions affected by 5-LO inhibition, further treatment options are needed. The instant invention addresses that need by providing novel 5-LO inhibitors which are useful for inhibiting leukotriene biosynthesis.